Antarctic bacteria provide a useful model system for studying cold adaptation (15, 17, 31, 36). These organisms are generally represented by the psychrotrophs and psychrophiles, which have the ability to grow at 0° C. They can transcribe at this lower temperature both in vitro and in vivo (31). However, nothing much is known about the nature of promoter and regulatory elements from these bacteria or about the mechanism of transcription at lower temperatures. Most of the transcriptional studies thus far have been carried out with only mesophilic bacterium, and the RNA polymerase from these bacteria, including Escherichia coli, cannot transcribe at 0° C. A recent study from our laboratory has demonstrated that the RNA polymerase of the Antarctic psychrotrophic bacterium Pseudomonas syringae has can transcribe at 0° C. The polymerase from the bacterium was not only active at the low temperature but also could transcribe in vitro preferentially the cold-inducible gene of E. coli cspA from a supercoiled template (43). However, absolutely no information is available with regard to the characteristics of promoter sequence such as the −10 and −35 elements from the bacterium for such low temperature specific transcription. Neither is any information available for the in vivo recognition of promoter sequences by RNA polymerase from the cold-adapted P. syringae. Therefore, we initially attempted to identify the genes from the Antarctic P. syringae that are upregulated at low temperature, with the help of TnJ-mediated random genomic fusions of a prompter-less reporter gene, lacZ (23). One of the fusions that produced at least 10- to 14-fcp,ld more p-galactosida.sc at a low temperature (4° C.) was identified by cloning and sequencing of ca. 450 bp of DNA sequence proximal to the Tn5 insertion site. The fusion was in the hutU gene, which encodes for an enzyme urocanase of the histidine utilization pathway of bacteria (13, 23). A direct assay of urocanase activity from the P. syringae and a few more Antarctic Pseudomonas species and their comparison with the mesophilic P. putida suggested that the hutU gene is unregulated in the psychrotrophs but not in the mesophilic. Therefore, it appeared to us that the hutUgene might be a useful model for investigating the mechanism of gene regulation at low temperatures in the Antarctic bacterium. Accordingly, we cloned and sequenced the DNA encompassing the hut if gene, and its upstream and downstream regions and identified different open reading frames (ORFs) in the region. We also examined transcripts from bacterial cells grown at low (4° C.) and high (22° C.) temperatures by Northern and primer extension analyses, and we identified the transcription start sites and other putative regulatory elements of the hutU gene. Additionally, we compare here the deduced amino acid sequences of the urocanase from the psychrotrophic P. syringae and other bacteria, including the mesophilic P. putida, in order to examine the possible amino acid substitutions due to a low-temperature adaptation.